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Ohm's Law Calculator

Calculate voltage, current, resistance, and power using Ohm's Law

📋 How to use:

Enter any two values to calculate the remaining two. You can calculate voltage, current, resistance, and power using Ohm's Law formulas.

Ohm's Law Calculator Guide

An Ohm's law calculator solves relationships among voltage (V), current (I), resistance (R), and power (P). Enter any two to compute the others, then size parts with safe margins.

What is Ohm's Law Calculator?

The Ohm's law calculator helps students and makers plan circuits: DC calculations, resistor networks (series/parallel), and quick AC power estimates using RMS values and power factor when needed.

How to Use the Ohm's Law Calculator

  1. Enter any two of V, I, R, P.
  2. Calculate the remaining values.
  3. (Optional) pick series/parallel mode to combine resistors.
  4. Use AC power mode for RMS estimates with power factor.
  5. Select units (mA, kOhm, kW) for readable numbers.

Formulas & Methods

  • Ohm's law: V = I*R, I = V/R, R = V/I
  • Power: P = V*I = I^2*R = V^2/R
  • Series: R_T = sum R_i
  • Parallel: 1/R_T = sum (1/R_i) (two-resistor shortcut R_T = (R1*R2)/(R1+R2))
  • AC power: P = V_rms*I_rms*pf

Assumptions & limitations

  • Formulas assume resistive loads; inductors/capacitors need impedance math.
  • Use RMS values for AC; frequency effects are ignored.
  • Components have tolerance and temperature drift.

Examples

Example A — Solve V and P
I = 0.25 A, R = 48 ohm -> V = I*R = 12 V, P = V*I = 3 W (use >= 6 W rating).

Example B — Parallel resistors
R1 = 1 kohm, R2 = 2 kohm -> R_T = (1*2)/(1+2) kohm = 0.667 kohm.

| Task | Formula | Result | |---|---|---| | Current | I = V/R | e.g., 12/220 -> 0.055 A | | Power | P = V^2/R | 12^2/220 -> 0.655 W | | Series | sum R | 100 + 330 = 430 ohm |

Pro Tips & Best Practices

  • Verify assumptions with a meter before powering the circuit.
  • Derate resistors and regulators to keep temps in check.
  • Add fuses or current limits during bring-up.
  • Mind voltage ratings on caps and semiconductors.

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FAQ

Q: What is Ohm's law?

A: Voltage equals current times resistance: V = I*R.

Q: How do I calculate power?

A: Use P = VI; also P = I^2R or P = V^2/R for resistive loads.

Q: Series vs parallel resistors?

A: Series adds resistances; parallel adds reciprocals. Current and voltage divide differently in each.

Q: Can I use this for AC?

A: For basic estimates, yes with RMS values; detailed AC requires complex impedance.

Q: What safety margins should I use?

A: Derate components; choose wattage ratings 2x expected dissipation and verify with a multimeter.

Engineering note: SI units and single-phase RMS values assumed; for detailed AC, use complex impedance methods.

Call to Action

Enter known values and compute the rest—then size components with safe margins before you prototype.